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KVM: x86: Tie Intel and AMD behavior for MSR_TSC_AUX to guest CPU model 

Squish the Intel and AMD emulation of MSR_TSC_AUX together and tie it to
the guest CPU model instead of the host CPU behavior.  While not strictly
necessary to avoid guest breakage, emulating cross-vendor "architecture"
will provide consistent behavior for the guest, e.g. WRMSR fault behavior
won't change if the vCPU is migrated to a host with divergent behavior.

Note, the "new" kvm_is_supported_user_return_msr() checks do not add new
functionality on either SVM or VMX.  On SVM, the equivalent was
"tsc_aux_uret_slot < 0", and on VMX the check was buried in the
vmx_find_uret_msr() call at the find_uret_msr label.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-05-04 10:17:33 -07:00 committed by Paolo Bonzini
parent e5fda4bbad
commit 61a05d444d
4 changed files with 41 additions and 39 deletions
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5
arch/x86/include/asm/kvm_host.h
View File

@ -1781,6 +1781,11 @@ int kvm_add_user_return_msr(u32 msr);
int kvm_find_user_return_msr(u32 msr);
int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);
static inline bool kvm_is_supported_user_return_msr(u32 msr)
{
return kvm_find_user_return_msr(msr) >= 0;
}
u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);
u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc);

24
arch/x86/kvm/svm/svm.c
View File

@ -2663,12 +2663,6 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data |= (u64)svm->sysenter_esp_hi << 32;
break;
case MSR_TSC_AUX:
if (tsc_aux_uret_slot < 0)
return 1;
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
msr_info->data = svm->tsc_aux;
break;
/*
@ -2885,24 +2879,6 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
svm->sysenter_esp_hi = guest_cpuid_is_intel(vcpu) ? (data >> 32) : 0;
break;
case MSR_TSC_AUX:
if (tsc_aux_uret_slot < 0)
return 1;
if (!msr->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
/*
* Per Intel's SDM, bits 63:32 are reserved, but AMD's APM has
* incomplete and conflicting architectural behavior. Current
* AMD CPUs completely ignore bits 63:32, i.e. they aren't
* reserved and always read as zeros. Emulate AMD CPU behavior
* to avoid explosions if the vCPU is migrated from an AMD host
* to an Intel host.
*/
data = (u32)data;
/*
* TSC_AUX is usually changed only during boot and never read
* directly. Intercept TSC_AUX instead of exposing it to the

15
arch/x86/kvm/vmx/vmx.c
View File

@ -1981,12 +1981,6 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
goto find_uret_msr;
case MSR_IA32_DEBUGCTLMSR:
msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
break;
@ -2302,15 +2296,6 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
vmx->pt_desc.guest.addr_a[index / 2] = data;
break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
/* Check reserved bit, higher 32 bits should be zero */
if ((data >> 32) != 0)
return 1;
goto find_uret_msr;
case MSR_IA32_PERF_CAPABILITIES:
if (data && !vcpu_to_pmu(vcpu)->version)
return 1;

36
arch/x86/kvm/x86.c
View File

@ -1642,6 +1642,30 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
* invokes 64-bit SYSENTER.
*/
data = get_canonical(data, vcpu_virt_addr_bits(vcpu));
break;
case MSR_TSC_AUX:
if (!kvm_is_supported_user_return_msr(MSR_TSC_AUX))
return 1;
if (!host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
/*
* Per Intel's SDM, bits 63:32 are reserved, but AMD's APM has
* incomplete and conflicting architectural behavior. Current
* AMD CPUs completely ignore bits 63:32, i.e. they aren't
* reserved and always read as zeros. Enforce Intel's reserved
* bits check if and only if the guest CPU is Intel, and clear
* the bits in all other cases. This ensures cross-vendor
* migration will provide consistent behavior for the guest.
*/
if (guest_cpuid_is_intel(vcpu) && (data >> 32) != 0)
return 1;
data = (u32)data;
break;
}
msr.data = data;
@ -1678,6 +1702,18 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))
return KVM_MSR_RET_FILTERED;
switch (index) {
case MSR_TSC_AUX:
if (!kvm_is_supported_user_return_msr(MSR_TSC_AUX))
return 1;
if (!host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
return 1;
break;
}
msr.index = index;
msr.host_initiated = host_initiated;